Implantable medical devices are used to treat patients suffering from a variety of conditions. Examples of implantable medical devices are implantable pacemakers and implantable cardioverter-defibrillators (ICDs), which are electronic medical devices that monitor the electrical activity of the heart and provide electrical stimulation to one or more of the heart chambers, when necessary. For example, pacemakers are designed to sense arrhythmias, i.e., disturbances in heart rhythm, and in turn, provide appropriate electrical stimulation pulses, at a controlled rate, to selected chambers of the heart in order to correct the arrhythmias and restore the proper heart rhythm. The types of arrhythmias that may be detected and corrected by pacemakers include bradycardias, which are unusually slow heart rates, and certain tachycardias, which are unusually fast heart rates.
Implantable cardioverter-defibrillators (ICDs) also detect arrhythmias and provide appropriate electrical stimulation pulses to selected chambers of the heart to correct the abnormal heart rate. In contrast to pacemakers, however, an ICD can also provide pulses that are much stronger and less frequent. This is because ICDs are generally designed to correct fibrillation, which is a rapid, unsynchronized quivering of one or more heart chambers, and severe tachycardias, where the heartbeats are very fast but coordinated. To correct such arrhythmias, ICDs deliver low, moderate, or high-energy shocks to the heart.
Pacemakers and ICDs are preferably designed with shapes that are easily accepted by the patient's body while minimizing patient discomfort. As a result, the corners and edges of the devices are typically designed with generous radii to present a package having smoothly contoured surfaces. It is also desirable to minimize the volume and mass of the devices to further limit patient discomfort.
The electrical energy for the shocks delivered by ICDs is generated by delivering electrical current from a power source (battery) to charge capacitors with stored energy. The capacitors are capable of rapidly delivering that energy to the patient's heart. In order to provide timely therapy to the patient after the detection of ventricular fibrillation, for example, it is necessary to charge the capacitors with the required amount of energy as quickly as possible. Thus, the battery in an ICD must have a high rate capability to provide the necessary current to charge the capacitors. In addition, since ICDs are implanted in patients, the battery must be able to accommodate physical constraints on size and shape.
Batteries or cells are volumetrically constrained systems. The sizes or volumes of components that are contained within a battery (cathode, anode, separator, current collectors, electrolyte, etc.) cannot in total exceed the available volume of the battery case. The arrangement of the components affects the amount or density of active electrode material, which can be contained within the battery case.
Conventional lithium batteries can employ an electrode configuration sometimes referred to as the “jelly roll” design, in which anode, cathode and separator elements are overlaid and coiled up in a spiral wound form. Generally, a strip sheet of lithium or lithium alloy comprises the anode, a cathode material supported on a charge collecting metal screen comprises the cathode, and a sheet of non-woven material separates the anode and cathode elements. These elements are combined and wound to form a spiral. Typically, the battery configuration for such a wound electrode is cylindrical. An advantage of this design is no more anode material is needed than what is mated to cathode material in the jelly roll electrode configuration. Such designs therefore have the potential for an improved match between the cathode and anode components and improved uniformity of anode and cathode utilization during discharge.
Typically, a battery includes corrosive material (e.g., the electrolyte). Any leakage of the corrosive material may undesirably damage the battery and/or the electrical components of the device (e.g., the implantable medical device) that the battery is used with. Such damage may generally cause the device to function improperly or otherwise cause it to cease operating altogether. In addition, if used in a medical device surgically implanted within a patient's body, as described above, accessibility to the device may be difficult for repair or replacement.
One approach to isolating the corrosive material involves using an electrical feedthrough arrangement for the battery to function as an intermediary. The feedthrough arrangement is designed to provide electrical connection between the battery and the other electrical components of the implantable medical device, and to maintain environmental isolation between the corrosive material within the battery and the other electrical components within the device. This isolation is, in part, achieved by using feedthrough pins that are generally corrosion resistant. However, effectively coupling these pins to the one or more of the electrodes in contact with the corrosive material within the battery can be difficult.
Coupling between the pins and the electrodes, e.g., by coupling the pins to tabs extending from the electrodes, can be difficult for several reasons. One reason involves differences in the physical properties of the pins and the tabs. This dissimilarity in material properties can lead to brittle joints or other unacceptable performance-related problems. To address such problems, current coupling methods have often involved manipulating the tab and/or the feedthrough pin for initial retention purposes before using a coupling process (e.g., resistance spot welding) to achieve a secure joint between the tab and pin. Unfortunately, these methods have been found to be highly sensitive to manufacturing variability (e.g., based on surface conditions of the pin), resulting in unstable manufacturing yield.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.